Methods and nodes supporting cell change

ABSTRACT

The invention relates to a method for supporting cell change between frequency layers. The method is performed in a Radio Network node of a wireless communication network deploying two frequency layers. The Radio Network node serves a User Equipment in a cell of a first of the two frequency layers. The User Equipment is configured to perform measurements on the first frequency layer, and to exclude measurements on a second of the two frequency layers. The method comprises receiving information from the User Equipment related to a coverage of a target cell of the second frequency layer, and determining whether to change to the target cell based on the received information.

This application is a continuation of U.S. application Ser. No.13/643,193, filed Oct. 24, 2012, which was the National Stage ofInternational Application No. PCT/SE2012/050472, filed May 4, 2012,which claims the benefit of U.S. Provisional Application No. 61/483,217,filed May 6, 2011, the disclosures of all of which are herebyincorporated by reference herein in their entirety.

TECHNICAL FIELD

The disclosure relates to cell change, and more specifically to a methodfor supporting cell change between frequency layers in a UE and/or in aradio network node of a wireless communication network deploying atleast two frequency layers. The disclosure also relates to the UE andthe radio network node configured to support cell change.

BACKGROUND

3GPP Long Term Evolution (LTE) is the fourth-generation mobilecommunication technologies standard developed within the 3rd GenerationPartnership Project (3GPP) to improve the Universal MobileTelecommunication System (UMTS) standard to cope with futurerequirements in terms of improved services such as higher data rates,improved efficiency, and lowered costs. High Speed Downlink PacketAccess (HSDPA) and High Speed Uplink Packet Access (HSUPA), togetherreferred to as High Speed Packet Access (HSPA), are also mobilecommunication protocols developed to cope with higher data rates thanoriginal UMTS protocols were capable of. The Universal Terrestrial RadioAccess (UTRA) Network (UTRAN) is the radio access network of a UMTS andEvolved UTRAN (E-UTRAN) is the radio access network of an LTE system. Inan UTRAN and an E-UTRAN, a User Equipment (UE) is wirelessly connectedto a Radio Base Station (RBS) commonly referred to as a NodeB (NB) inUMTS, and as an evolved NodeB (eNodeB or eNB) in LTE. An RBS is ageneral term for a radio network node capable of transmitting radiosignals to a UE and receiving signals transmitted by a UE.

FIG. 1a illustrates a radio access network with an RBS 101 that serves aUE 103 in a cell 105. In UMTS, also referred to as a 3G system, a RadioNetwork Controller (RNC) 106 controls the RBS 101 and other neighboringRBSs, and is, among other things, in charge of management of radioresources in cells for which the RNC is responsible. The RNC is in turnalso connected to the core network. In GSM, also referred to as a 2Gsystem, the node controlling the RBS 101 is called a Base StationController (BSC) 106. FIG. 1b illustrates a radio access network in anLTE system, also referred to as a 4G system. An eNB 101 a serves a UE103 in the cell 105 a. The eNB 101 a is directly connected to the corenetwork. The eNB 101 a is also connected via an X2 interface to aneighboring eNB 101 b serving another cell 105 b.

Signal Measurements for Mobility

Signal measurements performed by a UE can be used for various purposes.In particular, these measurements may be used for mobility-related taskssuch as cell selection and reselection and handover, but also forpositioning, Self-Organized Network (SON) management, network planning,and Minimization of Drive Tests (MDT). Signal strength and signalquality are the general parameters used for signal measurements.

In UTRAN, the following three downlink neighbor cell measurements arespecified primarily for mobility purposes:

Common Pilot Channel (CPICH) Received Signal Code Power (RSCP)

UTRA carrier Received Signal Strength Indicator (RSSI)

CPICH Ec/No, where CPICH Ec/No=CPICH RSCP/carrier RSSI

The RSCP is measured by the UE on a cell-level basis, using the CPICH.The UTRA carrier RSSI is measured over the entire carrier. Itcorresponds to the total received power and noise from all cellsincluding serving cells on the same carrier. The above CPICHmeasurements are the main quantities used for mobility decisions.

In E-UTRAN the following two downlink neighbor cell measurements arespecified, also primarily for mobility purposes:

Reference Symbol Received Power (RSRP)

Reference Symbol Received Quality (RSRQ), where RSRQ=RSRP/carrier RSSI

RSRP in E-UTRAN is solely measured by the UE on a cell-level basis,using reference symbols (RS). The E-UTRA carrier RSSI is measured overthe configured measurement bandwidth up to the entire carrier bandwidth.Again, the RSSI is the total received power and noise from all cells,including serving cells, on the same carrier. These two RS basedmeasurements are also the main quantities that are likely to be used forthe mobility decisions.

In GSM the following measurement is specified:

GSM Broadcast Channel (BCCH) carrier RSSI

CDMA-2000 1×RTT is a 3G wireless technology based on Code DivisionMultiple Access (CDMA). CDMA-2000 1×RTT is a CDMA version of theIMT-2000 standard which was developed by the InternationalTelecommunication Union (ITU). In cdma2000 1×RTT system the followingquality measurement for mobility is specified:

CDMA2000 1×RTT Pilot Strength

In CDMA-2000 High Rate Packet Data (HRPD) system the following qualitymeasurement for mobility is specified:

CDMA2000 HRDP Pilot Strength

IEEE 802.16 is a series of Wireless Broadband standards authored by theInstitute of Electrical and Electronics Engineers (IEEE). In WiMAX(Worldwide Interoperability for Microwave Access) IEEE 802.16 systemsthe following measurements are used for mobility:

WiMAX Preamble Carrier to Interference and Noise Ratio (CINR)

WiMAX RSSI.

WiMAX Preamble CINR is the CINR of the WiMAX downlink preamble, measuredby the UE for a particular base station. This measurement quantityprovides information on the actual operating condition of the receiver,including interference and noise levels, and signal strength. Ittherefore depicts the cell quality and is analogous to RSRQ and CPICHEc/No in E-UTRAN and UTRAN respectively.

WiMAX RSSI is the Received Signal Strength Indicator measured by the UEfrom the downlink preamble for a particular base station. It correspondsto signal strength measurements RSCP in UTRAN or RSRP in E-UTRAN.

Neighbor cell measurements are typically averaged over a long timeperiod to filter out the effect of fast fading. The measurements maye.g., be averaged over a time period in the order of 200 milliseconds oreven longer. There is also a requirement on the UE to measure and reportneighbor cell measurements such as RSRP and RSRQ in E-UTRAN for acertain minimum number of cells. In both UTRAN and E-UTRAN therequirement is to measure eight cells, comprising one serving and sevenneighbor cells, on the serving carrier frequency. Such a measurement iscommonly termed an intra-frequency measurement.

Timing Measurements

UE timing measurements are e.g., used for fingerprinting positioning andObserved Time Difference Of Arrival (OTDOA) in LTE. However, suchmeasurements may also be used for mobility purposes, network planning,SON, and MDT.

The following non-satellite based UE timing measurements are currentlystandardized and can be used at least for positioning purposes in LTE:

UE Rx-Tx time difference, currently defined only for intra-frequencymeasurements. The UE Rx-Tx time difference is defined as TUE-Rx−TUE-Tx,where TUE-Rx is the UE received timing of downlink radio frame number ifrom the serving cell, defined by the first detected path in time, andTUE-Tx is the UE transmit timing of uplink radio frame number i.

Reference Signal Time Difference (RSTD), defined for intra- andinter-frequency measurements. RSTD is the relative timing differencebetween the neighbor cell j and the reference cell i, defined asTSubframeRxj−TSubframeRxi, where TSubframeRxj is the time when the UEreceives the start of one subframe from cell j, and TSubframeRxi is thetime when the UE receives the corresponding start of one subframe fromcell i that is closest in time to the subframe received from cell j. Thereference point for the observed subframe time difference shall be theantenna connector of the UE.

The following non-satellite based timing measurements are currentlystandardized and may be used for positioning in UTRAN (3GPP TS 25.215,v10.0.0, 5.1.8-5.1.10, 5.2.8, 5.2.10, 5.2.14):

UE measurements (3GPP TS 25.215, v10.0.0, 5.1.8-5.1.10)

SFN-CFN observed time difference

SFN-SFN observed time difference

UE Rx-Tx time difference

UTRAN measurements (3GPP TS 25.215, v10.0.0, 5.2.8, 5.2.10, 5.2.14)

Round trip time

PRACH Propagation delay

SFN-SFN observed time difference

Mobility Scenarios

Fundamentally, there are two kinds of UE mobility states:

Low activity state mobility such as cell reselection;

Connected state mobility such as handover, cell change order, RadioResource Control (RRC) re-direction upon connection release.

In LTE there is only one low activity mobility state called idle state.In HSPA there are the following low activity states:

Idle State

URA_PCH state (UTRAN Registration Area Paging Channel state)

CELL_PCH state (Cell Paging Channel state)

CELL_FACH state (Cell Forward Access Channel state)

In HSPA systems, the connected state is also called CELL_DCH state sinceat least one Dedicated Channel (DCH) is in operation, at least for themaintenance of the radio link quality.

In any low activity state, the UE autonomously performs cell reselectionwithout any direct intervention of the network. However, to some extentthe UE behavior in low activity mobility state scenario could still becontrolled by a number of broadcasted system parameters and performancespecifications. The handover on the other hand is fully controlled bythe network through explicit UE specific commands and by performancespecification. Similarly, a RRC re-direction upon connection releasemechanism is used by the network to re-direct the UE to change toanother cell which may belong to the Radio Access Technology (RAT) ofthe serving cell or to another RAT. In this case, the UE typically goesinto idle state upon receiving the ‘RRC re-direction upon connectionrelease’ command, searches for the indicated cell or RAT, and accessesthe new cell or RAT.

In both low activity state and connected state, the mobility decisionsare mainly based on the same types of downlink neighbor cellmeasurements that were discussed above.

Both UTRAN and E-UTRAN are frequency reuse-1 systems. This means thatthe geographically closest cells or adjacent neighbor cells operate onthe same carrier frequency. An operator may also deploy multiplefrequency layers or carriers within the same coverage area. Therefore,idle mode and connected mode mobility in both UTRAN and E-UTRAN could bebroadly classified into three main categories:

Intra-frequency mobility for low activity and connected states

Inter-frequency mobility for low activity and connected states

Inter-RAT mobility for low activity and connected states

In intra-frequency mobility, the UE moves between cells belonging to thesame carrier frequency. This is the most important mobility scenariosince it involves low cost in terms of delay, as mobility measurementscan be carried out in parallel with channel reception. In addition, anoperator would have at least one carrier at its disposal that theoperator would like to be efficiently utilized.

In inter-frequency mobility, the UE moves between cells belonging todifferent carrier frequencies but of the same RAT. This could beconsidered as the second most important scenario.

In inter-RAT mobility, the UE moves between cells that belong todifferent RATs such as between UMTS and GSM or vice versa, or betweenUMTS and LTE or vice versa.

Positioning Methods

The following positioning methods are available or are likely to beintroduced in the HSPA and LTE standard for both the control plane andthe user plane solution:

Fingerprinting or pattern matching;

Cell Identification (CID);

UE-assisted and network-based Enhanced CID (E-CID), includingnetwork-based angle of arrival (AoA);

UE-based and UE-assisted Assisted Global Navigation Satellite System(A-GNSS) including (Assisted Global Positioning System (A-GPS);

UE-assisted OTDOA.

Some of them are described below in more detail.

Fingerprinting or Pattern Matching:

The fingerprinting or pattern-matching-based positioning method ischaracterized by two main phases. During the first phase, which is theoffline phase, the location fingerprints are created by performing asite-survey. The site or the coverage area is sub-divided into arectangular grid of points. During the offline phase, one or more typesof measurements such as received signal strength, signal quality, pathloss, time difference of arrival, etc., from the serving and multipleneighboring cells are performed. That is, the UE measurements mentionedin the preceding sections can be used. Statistics of the obtainedmeasurement are used to create a database or 2-dimensional tablecontaining predetermined measurement values, which values are mapped tothe points of the grid. Thus, the vector of the measurement values at apoint on the grid is called the location fingerprint of that point.Measurements during the offline phase can either be obtained by using amobile terminal or by a suitable dedicated device, which is capable ofdetecting cells and performing the required measurements from thedetected cells. Thus, the objective of the offline training phase is tobuild the mobile user's location profile. During the second phase, orthe so-called online phase, the mobile terminal whose position is to bedetermined performs measurements, such as received signal strength, fromthe serving and several neighbor cells. The positioning node thencomputes the user's location, i.e., the location of the mobile terminal,by determining the best match between the mobile reported measurementsand those corresponding to the location fingerprints in the pre-defineddatabase. The best matching location fingerprint is then reported to themobile terminal as the estimated position.

E-CID Positioning:

E-CID positioning exploits the advantage of low-complexity and fastpositioning with Cell Identification (CID), which exploits the networkknowledge of geographical areas associated with cell identities, butenhances positioning further with more measurement types. With E-CID,the following sources of position information are involved: the CID andthe corresponding geographical description of the serving cell, theTiming Advance (TA) of the serving cell, and the CIDs and thecorresponding signal measurements of the cells (up to 32 cells in LTE,including the serving cell), as well as angle-of-arrival (AoA)measurements.

The following UE measurements can be utilized for E-CID in LTE: RSRP,RSRQ, and UE Rx-Tx time difference. The E-UTRAN measurements availablefor E-CID are eNodeB Rx-Tx time difference also called TA Type 2, TAType 1 being (eNodeB Rx-Tx time difference)+(UE Rx-Tx time difference),and uplink (UL) AoA. UE Rx-Tx measurements are typically used for theserving cell, while e.g., RSRP and RSRQ as well AoA can be utilized forany cell and can also be conducted on a frequency different from that ofthe serving cell.

UE E-CID measurements are reported by the UE to a positioning serversuch as the Evolved SMLC (E-SMLC) or the Secure User Plane Location(SUPL) Location Platform (SLP) in LTE, over the LTE Positioning Protocol(LPP). The E-UTRAN E-CID measurements are reported by the eNodeB to thepositioning node over the LPP Annex protocol (LPPa).

The UE may receive assistance data from the network. However, no LPPassistance for E-CID is currently specified in the standard.

OTDOA Positioning:

The OTDOA positioning method makes use of the measured timing ofdownlink signals received from multiple eNodeBs at the UE. The UEmeasures the timing of the received signals using assistance datareceived from the positioning node, and the resulting measurements areused to locate the UE in relation to the neighboring eNodeBs.

With OTDOA, a UE measures the timing differences for downlink referencesignals received from multiple distinct locations. For each neighborcell, the UE measures RSTD, which is the relative timing differencebetween neighbor cell and reference cell. The UE position estimate isthen found as the intersection of hyperbolas corresponding to themeasured RSTDs. At least three measurements from geographicallydispersed base stations with a good geometry are needed to solve for twocoordinates of the terminal and the receiver clock bias. In order tosolve for position, precise knowledge of the transmitter locations andtransmit timing offset is needed.

To enable positioning in LTE and to facilitate positioning measurementsof a proper quality and for a sufficient number of distinct locations,new physical signals dedicated for positioning, so called PositioningReference Signals (PRS) have been introduced and low-interferencepositioning subframes have been specified in 3GPP.

PRS are transmitted from one antenna port (R6) according to apre-defined pattern. A frequency shift that is a function of PhysicalCell Identity (PCI) can be applied to the specified PRS patterns togenerate orthogonal patterns that model the effective frequency reuse ofsix, making it possible to significantly reduce neighbor cellinterference on the measured PRS and thus improve positioningmeasurements. Even though PRS have been specifically designed forpositioning measurements and in general are characterized by bettersignal quality than other reference signals, the standard does notmandate using PRS. Other reference signals, e.g., Cell-specificReference Signals (CRS) could in principle also be used for positioningmeasurements.

PRS are transmitted in pre-defined positioning subframes grouped byseveral consecutive subframes, i.e., one positioning occasion.Positioning occasions occur periodically with a certain periodicity of Nsubframes, i.e., the time interval between two positioning occasions.The standardized periods N are 160, 320, 640, and 1280 ms, and thenumber of consecutive subframes may be 1, 2, 4, or 6.

Carrier Aggregation

To enhance peak-rates within a technology, multi-carrier or CarrierAggregation (CA) solutions are known. For example, it is possible to usemultiple 5 MHz carriers in HSPA to enhance the peak-rate within the HSPAnetwork. Similarly, in LTE, multiple 20 MHz carriers may for example beaggregated in the UL and/or the downlink (DL). Each carrier in amulti-carrier or CA system is generally termed as a component carrier(CC), or sometimes also as a cell. In simple words, the CC means anindividual carrier in a multi-carrier system. CA is sometimes calledmulti-cell operation, multi-carrier operation, or multi-carriertransmission and/or reception. This means that CA can be used fortransmission of signals and data in UL and DL. In a CA deployment, oneof the CCs is the primary CC/cell or anchor CC/cell, while the remainingones are called secondary or supplementary CCs/cells. Generally, theprimary or anchor CC/cell carries the essential UE-specific signaling.The primary CC/cell exists in both UL and DL. The network may assigndifferent primary CCs/cells to different UEs operating in the samesector or cell.

The CCs/cells belonging to the CA system may belong to the samefrequency band, so called intra-band CA, or to different frequencybands, so called inter-band CA, or any combination thereof such as twoCCs/cells in band A and one CC/cell in band B. The inter-band CAcomprising of CCs/cells distributed over two bands is also calleddual-band-dual-carrier-HSDPA (DB-DC-HSDPA) in HSPA, or inter-band CA inLTE. Furthermore, the CCs/cells in intra-band CA may be adjacent ornon-adjacent in the frequency domain, which is also known as intra-bandnon-adjacent CA. A hybrid CA comprising of intra-band adjacent,intra-band non-adjacent and inter-band is also possible. Using carrieraggregation between carriers of different technologies is also referredto as multi-RAT CA, or multi-RAT-multi-carrier system, or simplyinter-RAT CA. For example, the carriers from UMTS and LTE may beaggregated. Another example is the aggregation of LTE and CDMA2000carriers. For the sake of clarity, CA within a same technology asdescribed above may be called intra-RAT or simply single RAT CA.

Problem Description

It is not mandatory for 3GPP Release 8 multi-mode UEs to support UTRA toE-UTRA measurements in CELL_DCH state. There is a feature groupindicator that can indicate whether or not such a measurement issupported by the UE. Hence, the network may not have E-UTRANmeasurements carried out by the UE as a basis for a decision on when tohandover or redirect the UE to a E-UTRAN cell. Such a decision thenbecomes blind, and may result in the UE being forced to revert to UTRANor GSM in the event that the E-UTRAN cell coverage is bad in the areawhere the UE is when it receives the handover or connection release withredirection command.

Furthermore, there is no support for UTRA to E-UTRA measurements for UEsin Cell_FACH state in 3GPP Releases 8 to 10. Hence, a UE in theCELL_FACH state camping on a UTRAN cell cannot reselect an E-UTRAN cell.At the same time, it has been observed that a UE may stay longer in theCELL_FACH state than what was initially assumed in the standardization.Therefore, the UE may get stuck in UTRA even though it may be in goodcoverage of a higher prioritized E-UTRAN carrier.

Circuit Switched Fallback (CSFB) is introduced in 3GPP Release 8 toallow an UE in LTE to reuse circuit switched domain services by defininghow the UE can switch its radio from an E-UTRAN access to another RATaccess such as GSM or UTRAN access that can support circuit switcheddomain services. In CSFB scenarios, the UE is connected to or camping onan E-UTRAN cell, and is redirected, e.g., to an UTRAN cell when the UEreceives an incoming call. This UTRAN cell might not have been measuredbefore by the UE, and in order to minimize the interruption time, theeNB may tunnel system information for the target cell in UTRAN. However,the UE still needs to detect the cell. In case of several neighbor UTRANcells it may take the UE some time to find the target cell if it is notthe strongest cell on that carrier as perceived by the UE.

SUMMARY

It is therefore an object to address some of the problems outlinedabove, and to provide a solution for improving cell change proceduresbetween frequency layers or carriers. This object and others areachieved by the methods, the radio network node and the UE according tothe independent claims, and by the embodiments according to thedependent claims.

In accordance with a first embodiment, a method in a radio network nodeof a wireless communication network deploying at least two frequencylayers is provided. The radio network node serves a user equipment in acell of a first of the at least two frequency layers. The user equipmentis configured to perform measurements on cells of the first frequencylayer, and to exclude measurements on cells of a second of the at leasttwo frequency layers. The method for supporting cell change betweenfrequency layers comprises receiving measurement results from the userequipment, for measurements performed on at least one cell of the firstfrequency layer. The method further comprises determining a location ofthe user equipment based on the received measurement results. The methodalso comprises assessing a coverage of a target cell of the secondfrequency layer based on the determined location and a coverage map forthe at least two frequency layers. Further, the method comprisesdetermining whether to change to the target cell based on the assessmentof the target cell coverage.

In accordance with a second embodiment, a radio network node for awireless communication network deploying at least two frequency layersis provided. The radio network node is configured to serve a userequipment in a cell of a first of the at least two frequency layers, andto support cell change between frequency layers. The user equipment isconfigured to perform measurements on cells of the first frequencylayer, and to exclude measurements on cells of a second of the at leasttwo frequency layers. The radio network node comprises a receiverconfigured to receive measurement results from the user equipment, formeasurements performed on at least one cell of the first frequencylayer. The radio network node further comprises a processing circuitconfigured to determine a location of the user equipment based on thereceived measurement results, and to assess a coverage of a target cellof the second frequency layer based on the determined location and acoverage map for the at least two frequency layers. The processingcircuit is further configured to determine whether to change to thetarget cell based on the assessment of the target cell coverage.

In accordance with a third embodiment, a method in a user equipment of awireless communication network deploying at least two frequency layersis provided. The user equipment is served in a cell of a first of the atleast two frequency layers by a radio network node and is configured toperform measurements on cells of the first frequency layer and toexclude measurements on cells of a second of the at least two frequencylayers. The method for supporting cell change between frequency layerscomprises performing measurements on at least one cell of the firstfrequency layer, and determining a location of the user equipment basedon results from the performed measurements. The method further comprisesassessing a coverage of a target cell of the second frequency layerbased on the determined location and a coverage map for the at least twofrequency layers. The method also comprises transmitting informationrelated to the assessed coverage of the target cell to the radio networknode.

Furthermore, in accordance with the third embodiment, a method in aradio network node of a wireless communication network deploying atleast two frequency layers is provided. The radio network node serves auser equipment in a cell of a first of the at least two frequencylayers. The user equipment is configured to perform measurements oncells of the first frequency layer, and to exclude measurements on cellsof a second of the at least two frequency layers. The method forsupporting cell change between frequency layers comprises receivinginformation from the user equipment related to a coverage of a targetcell of the second frequency layer, and determining whether to change tothe target cell based on the received information.

In accordance with a fourth embodiment, a user equipment for a wirelesscommunication network deploying at least two frequency layers configuredto support cell change between frequency layers is provided. The userequipment is configured to be served in a cell of a first of the atleast two frequency layers by a radio network node and to performmeasurements on cells of the first frequency layer and to excludemeasurements on cells of a second of the at least two frequency layers.The user equipment comprises a processing circuit configured to performmeasurements on at least one cell of the first frequency layer, todetermine a location of the user equipment based on results from theperformed measurements, and to assess a coverage of a target cell of thesecond frequency layer based on the determined location and a coveragemap for the at least two frequency layers. The user equipment furthercomprises a transmitter configured to transmit information related tothe assessed coverage of the target cell to the radio network node.

Furthermore, in accordance with the fourth embodiment, a radio networknode for a wireless communication network deploying at least twofrequency layers is provided. The radio network node is configured toserve a user equipment in a cell of a first of the at least twofrequency layers and to support cell change between frequency layers.The user equipment is configured to perform measurements on cells of thefirst frequency layer, and to exclude measurements on cells of a secondof the at least two frequency layers. The radio network node comprises areceiver configured to receive information from the user equipmentrelated to a coverage of a target cell of the second frequency layer.The radio network node also comprises a processing circuit configured todetermining whether to change to the target cell based on the receivedinformation.

In accordance with a fifth embodiment, a method in a user equipment of awireless communication network deploying at least two frequency layersis provided. The user equipment is camping on a cell of a first of theat least two frequency layers in idle mode and is configured to performmeasurements on cells of the first frequency layer and to excludemeasurements on cells of a second of the at least two frequency layers.The method for supporting cell change between frequency layers comprisesperforming measurements on at least one cell of the first frequencylayer, and determining a location of the user equipment based on resultsfrom the performed measurements. The method also comprises assessing acoverage of a target cell of the second frequency layer based on thedetermined location and a coverage map for the at least two frequencylayers, and determining whether to change to the target cell based onthe assessment of the target cell coverage.

In accordance with a sixth embodiment, a user equipment for a wirelesscommunication network deploying at least two frequency layers isprovided. The user equipment is configured to support cell changebetween frequency layers, to camp on a cell of a first of the at leasttwo frequency layers in idle mode, and to perform measurements on cellsof the first frequency layer and exclude measurements on cells of asecond of the at least two frequency layers. The user equipmentcomprises a memory and a processing circuit configured to performmeasurements on at least one cell of the first frequency layer, and todetermine a location of the user equipment based on results from theperformed measurements. The processing circuit is further configured toassess a coverage of a target cell of the second frequency layer basedon the determined location and a coverage map for the at least twofrequency layers, and to determine whether to change to the target cellbased on the assessment of the target cell coverage.

An advantage of embodiments is that they provide improved cell changeprocedures for mobility, such as a better alternative to a blindhandover and a connection release with blind redirection when the targetcell is not co-located with the source cell.

Another advantage of embodiments is that mobility is enhanced forRelease 8-10 UEs in CELL_FACH state, as they avoid getting stuck inUTRAN cells due to missing support of UTRA to E-UTRA measurements.

Other objects, advantages and features of embodiments will be explainedin the following detailed description when considered in conjunctionwith the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b are schematic illustrations of radio access networks.

FIG. 2 is a schematic illustration of non co-located cells on twofrequency layers F1 and F2.

FIG. 3 is a schematic illustration of a CA scenario.

FIG. 4 is a schematic illustration of how coverage of an unmeasured cellD can be expressed in distance from the measured cells A, B, and C.

FIGS. 5a-d are flowcharts illustrating methods according to embodiments.

FIGS. 6a-b are flowcharts illustrating the method in a radio networknode according to embodiments.

FIGS. 7a-b are flowcharts illustrating the method in a UE according toembodiments.

FIGS. 8a-b are flowcharts illustrating the method in a radio networknode according to embodiments.

FIGS. 9a-b are flowcharts illustrating the method in an idle mode UEaccording to embodiments.

FIG. 10 is a block diagram schematically illustrating a radio networknode according to embodiments.

FIG. 11 is a block diagram schematically illustrating a UE and a radionetwork node according to embodiments.

FIG. 12 is a block diagram schematically illustrating a UE according toembodiments.

FIG. 13 is a block diagram schematically illustrating a wirelesstransceiver apparatus with components relevant to embodiments of thepresent invention, as realized in either a UE or a radio base station.

DETAILED DESCRIPTION

In the following, different aspects will be described in more detailwith references to certain embodiments and to accompanying drawings. Forpurposes of explanation and not limitation, specific details are setforth, such as particular scenarios and techniques, in order to providea thorough understanding of the different embodiments. However, otherembodiments that depart from these specific details may also exist.

Moreover, those skilled in the art will appreciate that the functionsand means explained herein below may be implemented using softwarefunctioning in conjunction with a programmed microprocessor or generalpurpose computer, and/or using an Application Specific IntegratedCircuit (ASIC). It will also be appreciated that while the embodimentsare primarily described in the form of a method and a node, they mayalso be embodied in a computer program product as well as in a systemcomprising a computer processor and a memory coupled to the processor,wherein the memory is encoded with one or more programs that may performthe functions disclosed herein.

The techniques described herein improve a blind cell change, such as ablind handover and connection release with blind redirection, when thetarget cell is not co-located with the source cell. Embodiments of theinvention are described in a non-limiting general context in relation tothe following example scenarios:

-   -   1. Blind handover, redirect, or cell change order in a network        controlled mobility scenario;    -   2. Blind handover, redirect, or cell change order in a UE        controlled mobility scenario;    -   3. Blind configuration of a secondary CC in a CA or        multi-carrier scenario;    -   4. A CSFB scenario.

Although the above listed scenarios are examples when embodiments of theinvention are advantageous, there may be other cell change scenarios forboth idle mode and connected mode UEs in which embodiments of theinvention may be applied.

In the following, embodiments of the invention will be described withmore details, addressing mobility problems between 3G and 4G networkswhen the source and target cells are not co-located. In exemplaryembodiments, the network determines, for example using UE measurementsof 2G and 3G cells, whether the UE is within coverage of a 4G targetcell. This allows a UE to be handed over or redirected to E-UTRANwithout explicit E-UTRA measurements. More generally, a network node ora UE or a combination of both the network node and the UE determines,again based on UE measurements of one set of cells for one or morecarriers and one or more RATs, whether the UE is within coverage ofanother set of unmeasured target cells.

The network node may in one embodiment communicate with another networknode, such as a positioning node storing and maintaining a coverage map,to acquire the information related to the stored coverage map viasignaling means. In a variant of this embodiment, the determination ofthe target cell coverage may be performed fully or partially by the UE,in which case the coverage map may be maintained in the UE.

The different embodiments of the invention will hereinafter be describedwith reference to the different example scenarios listed above. However,first some common parts of the embodiments are described.

Common Parts

One aspect of the fundamental problem addressed is illustrated in FIG.2. Cells on different frequency layers or carriers, in FIG. 2illustrated by cells on 3G on carrier F1 and on 4G on carrier F2, arenot necessarily co-located. Hence, being at a particular distance from abase station in one layer does not mean that the UE is at the samedistance from a base station on another layer. One may also imagine thatcell sizes may differ on different layers. Further, a layer with smallcells may have both cells that are co-located with larger cells onanother carrier, but also additional cells in-between those sites inorder to achieve full coverage. In some environments, one layer may onlybe hosting hotspot coverage areas, whereas another layer is providingfull coverage providing mobility. The hotspot cells may be on asecondary CC (carrier F2) in the case of CA as illustrated in FIG. 3,where a primary CC (carrier F1) offers mobility and secondary CCs areavailable only at hotspots. However, hotspot cells may also be usedpurely for traffic load balancing. Thus embodiments of the invention arenot only applicable to strictly non-co-located deployment scenarios.

There are several existing methods for estimating a UE's location.Several of these methods were described above in the background section.The positioning method used in a given instance may depend on severalfactors, such as the UE's capabilities and the UE state. The network mayalso implement other methods than those mentioned above. Some examplesare:

-   -   A. Location estimated from a timing offset used by each base        station for dedicated transmissions using macro diversity. One        example is UMTS soft handover in CELL_DCH state, where a        Dedicated Physical Channel (DPCH) shall be received within ±        1/10th of a slot.    -   B. Location predicted based on a UE trail, such as recent        handovers and time between those handovers, and knowledge of        geography and/or topography. One example is when the UE is        detected to be travelling along a particular route.

It will be appreciated that any of the positioning methods describedhere or any other standardized or proprietary solution revealing the UElocation with good enough accuracy may be used for the techniquesdescribed here for determining whether there is coverage from anunmeasured cell.

A simplistic approach to determine from measurements on one carrierwhether there is cell coverage on another carrier is illustrated in FIG.4. Here, it is determined, from an estimated distance from an RBS 401a-c of each cell A, B and C on one carrier, whether the UE is withincoverage of the cell D on another carrier. The estimated distances tothe RBSs may be derived from timing offsets of signals received for thedifferent cells A, B, and C, or from signal strength levels (e.g., RSRP,RSCP) and/or signal quality levels (e.g., RSRQ, Ec/No). In FIG. 4 it isillustrated how the coverage of an unmeasured cell D, which is normallygiven by the circle 402, may be expressed in distances from the RBSs 401a-c derived from the measured cells A, B, and C. If the UE is at adistance from the RBS 401 a serving cell A which is greater than a1 andsmaller than a2, and at a distance from the RBS 401 b serving cell Bwhich is greater than b1 and smaller than b2, and at a distance from theRBS 401 c serving cell C which is greater than c1 and smaller than c2,the UE is within the area 403 which is thus within the coverage area 402of cell D.

In a more sophisticated approach, some entity in the network maintains acoverage map for intra-RAT and inter-RAT carriers with overlappingcoverage. In the case of UTRA this entity may be the RNC, and in thecase of E-UTRA, it may be the eNodeB. The particular deployment of thecoverage map is not particularly important, as long as it accessible tothe entity that seeks to determine whether there is coverage from anunmeasured cell. The entity may be a network node or the UE itself aswill be described below. When e.g., the network receives updatedinformation on the UE location, the coverage map(s) is checked to seewhether there are cells with good coverage on other carriers potentiallybelonging to other RATs in that location. The coverage map may e.g.,provide a mapping between signal strength values for the differentfrequency layers or carriers in a specified location. One example is amapping between the CPICH RSCP value for a UTRA cell in a certainlocation and the corresponding RSRP value for a E-UTRA cell. The mappingof other parameter values such as quality measure values may also beprovided by the coverage map. Examples of signal quality measures areCPICH Ec/No for a UTRA cell and RSRQ for a E-UTRA cell. Based on acombination of factors, such as a predicted quality of the coverageobtained from the coverage map and the UE location, and a priority ofthe other carriers relative to the priority of the currentintra-frequency carrier, the network may take a decision to move the UEfrom a cell on one carrier to a cell on another carrier.

Maintenance of the coverage map(s) may be carried out in several ways,both off-line and online. The following is a non-limiting list ofexamples of how to maintain the coverage map(s). Any of the followingtechniques may be used in combination with any other one:

The network operator may conduct simultaneous measurements on theconcerned carriers in drive tests;

The network operator may every now and then configure UEs with fullmeasurement capabilities to conduct measurements on all concernedcarriers, or at least on intra-frequency carrier and higher prioritizedcarrier(s). The results may then be used to update the coverage maps;

The network operator may assess statistics on the number of revertsafter handover/redirection to see whether the coverage map(s) should berevised for some locations;

The network operator may use information from MDT-capable devices;

The network operator may use radio propagation simulations and/orcalculations as a basis for maintaining the coverage map(s).

Hereinafter, the different embodiments of the invention will bedescribed with reference to the four example scenarios listed above.

Scenario 1: Blind Handover, Redirect, or Cell Change Order in aNetwork-Controlled Mobility Scenario

This scenario is described with reference to FIG. 5a . The UE is withinan area where there is coverage on several carriers. The network hasconfigured the UE to carry out measurements on cells of one or morefrequency layers or carriers, but is excluding measurements on cells ofat least one frequency layer or carrier. There may be several reasons towhy cells of a carrier are excluded from measurements. One reason may bethat the measurement capabilities of the UE are restricted. As mentionedabove, it is e.g., not mandatory for 3GPP Release 8 multi-mode UEs tosupport UTRA to E-UTRA measurements. In such a case, the UE may thussupport both 3G and 4G but does not support UTRA to E-UTRA measurementsin CELL_DCH state, and a mobility decision from 4G to 3G must thus beblind.

In step 501, the UE reports measurement results to the network. This isdone periodically to keep the measurement result reports up to date.Based on the measurement results, the network may determine the locationof the UE, in step 502. Any of the positioning methods described hereinmay e.g., be used to determine the UE location. In step 503 the networkassesses the coverage of a potential target cell on the unmeasuredfrequency layer/carrier which may be a more highly prioritized frequencylayer/carrier, using the determined UE location and the coverage map. Asan example, an RSRQ value for an E-UTRAN cell in the UE location isderived from the coverage map. If the derived RSRQ value is above athreshold and the UE thus is expected to receive the unmeasured cellwith good quality (see 504/Yes), the network issues a cell changecommand to the UE in step 505. The cell change command may be a commandfor handover, release with redirection, or cell change order.

However, if the UE is not expected to receive the unmeasured cell withgood quality, e.g., if the RSRQ value is below the threshold (see504/No), a normal mobility evaluation based on the measured carriers isexecuted in steps 506 and 507. If it is determined that a cell changeshould be performed in the normal mobility evaluation (507/Yes), theresult is a handover, a release with redirection, or a cell change orderto a measured cell in step 508. In the event that the mobilityevaluation does not result in a handover, a release with redirect, or acell change order to a measured cell (see 507/No), the network waits forthe next measurement report, or longer time than that, to again assesswhether the UE is likely to be within good coverage of an unmeasuredfrequency layer cell. Steps 501-504 are thus repeated. The time thenetwork waits before it performs the next assessment of whether the UEis likely to be within good coverage of the unmeasured frequency layercell, may depend on UE history as determined from past reports and/oractivities, such as if the UE has been stationary or mobile.

Depending on the location method used, it may not be necessary to orderthe UE to send periodic measurement reports. If the base station usessignals received on the UL to determine location of the UE, i.e.determines location based on time of arrival measurements, it issufficient to request event-triggered reporting for supporting mobilitybased only on the measured carriers.

Scenario 2: Blind Handover/Redirection/Cell Change Order in aUE-Controlled Mobility Scenario

This scenario is described with reference to FIG. 5b . Also here, the UEis within an area where there is coverage on several carriers. Thenetwork has configured the UE to carry out measurements on cells of oneor more frequency layers or carriers, but is excluding measurements oncells of at least one frequency layer or carrier. There may be severalreasons to why cells of a carrier are excluded from measurements. Onereason may be that the measurement capabilities of the UE arerestricted. As mentioned above, Release 8-10 terminals may get stuck inUTRA due to missing support of UTRA to E-UTRA measurements when the UEis in CELL_FACH state, as 3G to 4G mobility is not possible in this UEstate.

In step 511, the UE reports measurement results to the network. This isdone periodically to keep the measurement result reports up to date. Inthe case of UTRA, this could be periodic Random Access Channel (RACH)measurement reports of the monitored set of cells in CELL_FACH state.Based on the measurement results, the network may determine the locationof the UE, in step 512. As an example, any of the positioning methodsdescribed herein may be used to determine the UE location. In step 513the network assesses the coverage of a potential target cell on theunmeasured frequency layer/carrier which may be a more highlyprioritized frequency layer/carrier, using the determined UE locationand the coverage map. As an example, an RSRQ value for an E-UTRAN cellin the UE location is derived from the coverage map. If the derived RSRQvalue is above a threshold and the UE thus is expected to receive theunmeasured cell with good quality (see 514/Yes), the network issues ahandover, release with redirect, or cell change order to the UE in step515. This may involve the network changing UE state before executingaforementioned operation.

However, if the UE is not expected to receive the unmeasured cell withgood quality, e.g., if the RSRQ value is below the threshold (see504/No), the network waits for the next measurement report, or longertime than that, to again assess whether the UE is likely to be withingood coverage of an unmeasured frequency layer cell. Steps 511-514 arethus repeated. The time the network waits before it performs the nextassessment of whether the UE is likely to be within good coverage of theunmeasured frequency layer cell, may depend on UE history as determinedfrom past reports and/or activities, such as if the UE has beenstationary or mobile.

Depending on the location method used, it may not be necessary to orderthe UE to send periodic measurement reports. If the base station usessignals received on the UL to determine location of the UE, i.e.determines location based on time of arrival measurements, it issufficient to request event-triggered reporting for supporting mobilitybased only on the measured carriers.

Scenario 3: Blind Configuration of Secondary CC in CA or Multi-CarrierScenario

This scenario is described with reference to FIG. 5c . Here, the UE iswithin an area where CA or multi-carrier is supported. The UE isconnected to a primary cell or anchor cell on a primary CC (PCC). Theprimary cell is a macro cell that covers a wide area and thus providesmobility. In this area there are also several secondary cells on asecondary CC (SCC). The secondary cells are smaller cells than theprimary cell and the SCC does not provide coverage over the completearea. The network has configured the UE with measurements on PCC, butnot on SCC which is thus “non-configured”. In this scenario, embodimentsof the invention may thus be used in a CA scenario to determine whetherthe UE is within a “hotspot” secondary cell's coverage when connected toa macro primary cell without actually having the UE to measure thesecondary cell.

In step 521, the UE reports measurement results to the network. This isdone periodically to keep the measurement result reports up to date.Based on the measurement results, the network may determine the locationof the UE, in step 522. As an example, any of the positioning methodsdescribed herein may be used to determine the UE location. In step 523the network assesses the coverage of a potential secondary cell on theunmeasured SCC, using the determined UE location and the coverage map.If the UE is expected to receive the unmeasured secondary cell with goodquality (see 524/Yes), the network may change cell, meaning that itconfigures the SCC in 525, which was previously non-configured. The UEwill after the SCC configuration thus have to do measurements on the SCCas a preparation to receive data on SCC in short notice.

However, if the UE is not expected to receive the unmeasured secondarycell with good quality (see 524/No), the network waits for the nextmeasurement report, or longer time than that, to again assess whetherthe UE is likely to be within good coverage of an unmeasured frequencylayer cell. Steps 521-524 are thus repeated. The time the network waitsbefore it performs the next assessment of whether the UE is likely to bewithin good coverage of the unmeasured frequency layer cell, may dependon UE history as determined from past reports and/or activities, such asif the UE has been stationary or mobile.

Depending on the location method used, it may not be necessary to orderthe UE to send periodic measurement reports. If the base station usessignals received on the UL to determine location of the UE, i.e.determines location based on time of arrival measurements, it issufficient to request event-triggered reporting for supporting mobilitybased only on the measured carriers.

In the case of E-UTRA, the above described embodiments may beparticularly interesting for non-configured secondary cell measurementsin intra-band as well as inter-band CA. This is due to that all mobilityis to be based on the primary cell alone, and non-configured secondarycells are in some cases to be measured using measurement gaps, whereasconfigured secondary cells may be measured without gaps. The measurementgaps puncture the serving primary cell communication and thus reduce thethroughput. Hence by avoiding measurements of non-configured secondarycells it may be possible to increase the throughput in the primary cellwhen the UE has bad coverage on the secondary cell.

Scenario 4: Improved Circuit-Switched Fallback Scenario

This scenario is described with reference to FIG. 5d . Here, a UE isconnected to or, if in idle mode, camping on an E-UTRA cell in a networkthat does not contain a gateway between circuit-switched (CS) andpacket-switched (PS) domains. Such a gateway is needed to allow forVoice over IP (VoIP) calls in E-UTRA. The UE has not been configuredwith measurements on 2G or 3G carriers and has thus not carried out anyinter-RAT measurements.

In step 531, the network detects an incoming voice call that is to beterminated by the UE. In case the UE is in idle state, the network willpage the UE by which it enters the connected state. The networkdetermines the UE location in step 532.

In case the UE already was in connected state, the network may alreadyhave information on a UE position from past measurements or ULtransmissions. Otherwise it determines the position based on the latestmeasurement. In case the UE recently was in idle mode, the network maynot have full knowledge on the UE location. However, the UE can belocated while engaged in random access. For example the network canperform measurements on the uplink received signal sent by the UE on therandom access channel. Example of measurements which can be performedare one way propagation delay, time of arrival of signal, UE Rx-Tx timedifference measurement, and Angle of Arrival (AoA) of signals. Thenetwork can use these measurements to determine the location of the UEat the time of random access.

The network determines, in step 533, the best target 3G or 2G cell withrespect to the determined UE location by using the coverage map, andissues, in step 534, a handover, a release with redirection or a cellchange order to that cell. Tunneling of system information may or maynot be done at the same time. Since the target 2G or 3G cell is the bestor the strongest cell at the UE position, the UE will find it quicklyalthough it may not be co-located with the E-UTRA source cell. The delayis thus minimized.

This is an example of a service-triggered mobility for which a low setupdelay and interruption time is needed. Another example of when low delayand short interruption time is needed is for congestion-triggeredmobility.

Signaling Means Between Radio Network Node and Network Node StoringCoverage Maps

As discussed above, in order to assess the coverage of a cell on anunmeasured frequency layer or carrier the network uses the UE's locationand the coverage map. The coverage map may be stored and maintained indifferent entities or nodes. Embodiments of the invention thereforeinvolve a signaling exchange between e.g., the serving radio networknode and another node containing the coverage maps, as describedhereinafter.

In existing systems, pre-defined coverage maps are generally located ina positioning node or in a dedicated server. These coverage maps may beused for positioning methods like fingerprinting. For example, in LTEthe coverage maps can reside in the E-SMLC, which is the positioningnode. In several of the scenarios described above, a radio network node,such as the eNodeB in LTE or the RNC in HSPA, performs the mobilitydecision, e.g., the handover. Thus, in some embodiments of the presentinvention, the radio network node acquires one or more sets ofinformation associated with the coverage map related to the target cellsof the unmeasured frequency layer or carrier F2. The acquiredinformation requires signaling between the radio network node and thenode which contains the data base or coverage map.

The signaled information may comprise for example the expected signalvalue for the target frequency layer F2 associated with the measuredsignal value on the source frequency layer F1. The signal value may be asignal strength or a signal quality value. The signaled information mayalternatively comprise an offset which is a function of the measuredsignal value on the source frequency layer F1 and the correspondingvalue on the target frequency layer F2. The advantage is that thesignaling of an offset reduces the signaling overhead.

In still another alternative, the signaled information may comprise anoffset which is a function of the measured signal value on the sourcefrequency layer F1, the corresponding signal value on the targetfrequency layer F2, and a reference value. The frequency layers F1 andF2 may belong to the same or different frequency bands. In case ofdifferent bands the difference between the frequencies can be verylarge, e.g., if F1 and F2 belong to band 1 (2100 MHz) and band 8 (900MHz) respectively. The dependency of carrier frequency on the coverageor path loss is well known. Therefore path loss, which depends uponfrequency, may also be very different in case of large differencebetween frequencies. The coverage is significantly better at lowercarrier frequencies. According to the free space model the frequencydependency on path loss is given by (1):

$\begin{matrix}{{\Delta\; L} = {20\;{\log_{10}( \frac{F_{1}}{F_{2}} )}}} & (1)\end{matrix}$where ΔL is the path loss difference between carrier frequencies F1 andF2 assuming the same distance between the transmitter and receiver.

Assuming F1=1800 MHz and F2=900 MHz then according to (1) the path lossdifference in free space is approximately 6 dB. Assuming F1=2100 MHz andF2=900 MHz then the path loss difference in free space is even largeri.e. approximately 7 dB. For the frequencies F1 and F2 in bands 450 MHzand 3500 MHz respectively in free space the difference is approximately18 dB. The reference value can therefore be used to compensate for suchdiscrepancy due to the large frequency difference.

UE-Based Method for Determining Coverage of Non-Measured FrequencyLayers

In the above embodiments described with reference to scenario 1-4, aradio network node receives the measurements, determines the location ofthe UE based on the measurements, and assesses the coverage of cells ofa non-measured frequency layer, in order to decide whether to perform acell change to the non-measured frequency layer. However, in alternativeembodiments, the method is performed by the radio network node and theUE in cooperation, as will be described hereinafter.

In this exemplary alternative embodiment of the invention, the UEmaintains the coverage map database. Such a database may be used for aUE-based positioning method. The database can be updated by the UE byperforming measurements in the background, or it may be updated by thenetwork. It can be used for all the mobility scenarios 1-4 describedabove.

The UE performs measurements on cells of one frequency layer or RAT suchas the serving RAT, and determines its location from the measurements.The UE then uses the coverage map to assess the coverage of a targetcell of another RAT. Based on this assessment, the UE reports a derivedvalue of a measurement on the target cell to the radio network node. Thereporting of the derived value of the target cell may be sent inresponse to a request from the network. The network in turn uses thereceived report results for performing one or more of the requiredmobility tasks described above.

According to one embodiment, the UE may also report to the network itscapability to support such a feature, i.e., the capability to providederived measurement results for a certain target cell on a frequencylayer without performing the actual measurement on that frequency layer.The capability information may be used by the network for severalpurposes, such as to avoid configuring measurement gaps for certainfrequency layers or RATs.

In still another alternative embodiment, relevant when the UE is in idlemode, the method is entirely performed by the UE, as it is the UE thatdecides about any mobility measures in terms of cell reselection when inidle mode. The UE thus performs the measurements, determines itslocation, assesses the coverage of a target cell of an unmeasuredfrequency layer based on the location and the coverage map, andeventually also determines whether to perform a cell reselection basedon the assessed coverage.

The method is thus the same in all three alternative embodiments,although different nodes are involved in the different embodiments:Determine a UE location based on UE measurements of one set of cells forone or more carriers and one or more RATs, and to assess based on thedetermined UE location and a coverage map whether the UE is withincoverage of a set of unmeasured target cells. This is done to decidewhether to change to a target cell of an unmeasured frequency layer. Thepurpose is the same in all three embodiments, i.e. to improve cellchange procedures for mobility between frequency layers.

Methods and Nodes

FIGS. 6a-b , illustrates the method performed in the radio network node.FIG. 6a is a flowchart illustrating a first embodiment of a method in aradio network node for supporting cell change between frequency layers.The cell change may comprise a cell reselection, a handover, or aconnection release with redirection. The radio network node is part of awireless communication network in which at least two frequency layers,F1 and F2, are deployed, e.g., as described earlier with reference toFIG. 2 or 3. The radio network node may e.g., be a NodeB in an UTRAN(see FIG. 1a ). The radio network node 101 serves a UE 103 in a cell 105of a first of the at least two frequency layers F1, the UE beingconfigured to perform measurements on cells of the first frequency layerF1, and to exclude measurements on cells of a second of the at least twofrequency layers F2. The method comprises:

610: Receiving measurement results from the UE, for measurementsperformed on at least one cell of the first frequency layer F1. ForUTRAN, the measurement results may e.g., comprise CPICH RSCP and RSSImeasurements.

620: Determining a location of the UE based on the received measurementresults. A fingerprinting method may e.g., be used to determine the UElocation as already described above.

630: Assessing a coverage of a target cell of the second frequency layerF2 based on the determined location and a coverage map for the at leasttwo frequency layers. The coverage map is checked to see whether thereare cells with good coverage on carrier F2 in that location.

640: Determining whether to change to the target cell based on theassessment of the target cell coverage. In an exemplary embodiment, theradio network node determines to change to the target cell when it isassessed that the target cell will be received with a quality which isequal to or above a threshold. With a quality above a certain threshold,coverage is good on F2, and if coverage is good and F2 is a prioritizedcarrier, a cell change may be initiated.

FIG. 6b is a flowchart illustrating another embodiment of the method inthe radio network node. The step of assessing 630 the coverage of thetarget cell of the second frequency layer based on the determinedlocation and the coverage map comprises deriving 631 from the coveragemap a signal strength or signal quality value for the second frequencylayer corresponding to the determined location. One example is a mappingbetween the CPICH RSCP value for the UTRA cell on carrier F1 in the UElocation and the corresponding RSRP value for a E-UTRA cell on carrierF2. Deriving 631 the signal strength or signal quality value from thecoverage map does in embodiments comprise receiving one of the followingfrom a network node comprising the coverage map:

the signal strength or signal quality value for the second frequencylayer, or

an offset which is a function of the signal strength or signal qualityvalue for the second frequency layer and the associated signal strengthor signal quality value for the first frequency layer.

The coverage map may in the UTRAN network be maintained in the RNC, and

deriving the signal strength from the coverage map would thereforeinvolve receiving it from the RNC. By sending the offset, the signalingcapacity is reduced compared to sending the actual value.

In step 640, the radio network node may e.g., determine to change to thetarget cell when it is assessed that the target cell will be receivedwith a quality which is equal to or above a threshold. The method mayalso comprise the further step, in 660, of performing an evaluation ofmobility within the first frequency layer F1 based on the measurementson the cells of the first frequency layer, when it is assessed that thetarget cell will be received with a quality which is below thethreshold. In this case the F2 coverage is not good enough for the UE tochange to the F2 carrier, and a normal intra-RAT mobility assessment maythus be performed, as already described above with reference to FIG. 5a.

When the radio network node has determined to change to the target cell,the method may comprise the further step, in 650, of issuing an order tochange to the target cell.

In a scenario corresponding to scenario 3 described previously, themeasured cell of the first frequency layer F1 is a primary cell and thetarget cell is a secondary cell in a multi-carrier network. In thisembodiment, determining whether to change to the secondary cellcomprises determining whether to configure the secondary cell formulticarrier operation based on the assessment of the secondary cellcoverage. As explained above, this makes it possible to configuresecondary cells when the UE is within coverage without having to measurethem first. This is an advantage, as measuring non-configured secondarycells in some cases require a measurement gap configuration whichreduces capacity.

FIGS. 7a-b and FIGS. 8a-b , illustrates the method performed in the UEand the radio network node in cooperation. FIG. 7a is a flowchartillustrating one embodiment of a method for supporting cell changebetween frequency layers, in a UE of a wireless communication networkdeploying at least two frequency layers F1, F2. The UE 103 is served ina cell of a first of the at least two frequency layers F1 by a radionetwork node 101, and is configured to perform measurements on cells ofthe first frequency layer F1 and to exclude measurements on cells of asecond of the at least two frequency layers F2. The method comprises:

710: Performing measurements on at least one cell of the first frequencylayer F1. For UTRAN, the measurements may e.g., comprise CPICH RSCP andRSSI measurements.

720: Determining a location of the UE based on the results from theperformed measurements. A fingerprinting method may e.g., be used todetermine the UE location as already described above.

730: Assessing a coverage of a target cell of the second frequency layerF2 based on the determined location and a coverage map for the at leasttwo frequency layers. The coverage map is checked to see whether thereare cells with good coverage on carrier F2 in that location.

740: Transmitting information related to the assessed coverage of thetarget cell to the radio network node.

FIG. 7b is a flowchart illustrating another embodiment of the method inthe UE. The step of assessing, in 730, the coverage of the target cellof the second frequency layer based on the determined location and thecoverage map comprises deriving, in 731, from the coverage map a signalstrength or signal quality value for the second frequency layercorresponding to the determined location. The coverage map may bereceived from the radio network node. Alternatively it may be maintainedin the UE itself. The information transmitted in 740, related to theassessed coverage of the target cell, comprises in one embodiment thederived signal strength or signal quality value.

In one embodiment, the method also comprises transmitting, in 750, acapability to the radio network node, wherein the capability indicatesthat the UE supports assessment of coverage of cells of the secondfrequency layer without performing measurements on said cells. In thisway, the radio network node knows that it can request the UE to performthe coverage assessment of unmeasured cells.

FIG. 8a is a flowchart illustrating one embodiment of a method forsupporting cell change between frequency layers, in a radio network nodeof a wireless communication network deploying at least two frequencylayers F1 and F2. The cell change may comprise a cell reselection, ahandover, or a connection release with redirection. The radio networknode serves a UE 103 in a cell of a first of the at least two frequencylayers F1. The UE is configured to perform measurements on cells of thefirst frequency layer F1, and to exclude measurements on cells of asecond of the at least two frequency layers F2. The method comprises:

810: Receiving information from the UE related to a coverage of a targetcell of the second frequency layer F2. The radio network node thusreceives the result from the coverage assessment performed in the UE, asdescribed above with reference to FIG. 7 a.

820: Determining whether to change to the target cell based on thereceived information.

FIG. 8b is a flowchart illustrating another embodiment of the method inthe radio network node. The method further comprises receiving, in 830,a capability from the UE. The capability indicates that the UE supportsassessment of coverage of cells of the second frequency layer F2 withoutperforming measurements on said cells. The received capability maytrigger a request for information related to the coverage of the targetcell to the UE. Step 820 of determining whether to change to the targetcell comprises determining to change to the target cell when it isassessed that the target cell will be received with a quality which isequal to or above a threshold. When it is determined to change to thetarget cell, the method may further comprise issuing, in 850, an orderto change to the target cell. When it is assessed that the target cellwill be received with a quality which is below the threshold, and thusno change to the target cell will take place, the method comprises, in840, performing an evaluation of mobility within the first frequencylayer F1 based on the measurements on the cells of the first frequencylayer.

In a scenario corresponding to scenario 3 described previously, themeasured cell of the first frequency layer F1 is a primary cell and thetarget cell is a secondary cell in a multi-carrier network. In thisembodiment, determining whether to change to the secondary cellcomprises determining whether to configure the secondary cell formulticarrier operation based on the assessment of the secondary cellcoverage.

FIGS. 9a-b , illustrates the method performed in the UE only, when theUE is in idle mode. FIG. 9a is a flowchart illustrating one embodimentof a method for supporting cell change between frequency layers in a UEof a wireless communication network deploying at least two frequencylayers F1 and F2. In this embodiment, the UE is camping on a cell of afirst of the at least two frequency layers F1 in idle mode. The UE isconfigured to perform measurements on cells of the first frequency layerF1 and to exclude measurements on cells of a second of the at least twofrequency layers F2. The method comprises:

910: Performing measurements on at least one cell of the first frequencylayer F1.

920: Determining a location of the UE based on the results from theperformed measurements. A fingerprinting method may e.g., be used todetermine the UE location as already described above.

930: Assessing a coverage of a target cell of the second frequency layerbased on the determined location and a coverage map for the at least twofrequency layers. In one embodiment, illustrated in FIG. 9b , assessingthe coverage of the target cell of the second frequency layer F2comprises deriving, in 931, from the coverage map a signal strength orsignal quality value for the second frequency layer corresponding to thedetermined location.

940: Determining whether to change to the target cell based on theassessment of the target cell coverage.

An embodiment of a radio network node 1000 for a wireless communicationnetwork deploying at least two frequency layers is schematicallyillustrated in the block diagram in FIG. 10. The radio network node isconfigured to serve a UE 1050 in a cell of a first of the at least twofrequency layers, and to support cell change between frequency layers.The cell change may comprise a cell reselection, a handover, or aconnection release with redirection. The UE is configured to performmeasurements on cells of the first frequency layer, and to excludemeasurements on cells of a second of the at least two frequency layers.The radio network node comprises a receiver 1001 configured to receivemeasurement results from the UE, for measurements performed on at leastone cell of the first frequency layer. The receiver 1001 may beconnected via an antenna port to a same or to different receivingantennas 1008. The radio network node further comprises a processingcircuit 1002 configured to determine a location of the UE based on thereceived measurement results, and to assess a coverage of a target cellof the second frequency layer based on the determined location and acoverage map for the at least two frequency layers. The processingcircuit is also configured to determine whether to change to the targetcell based on the assessment of the target cell coverage.

In one embodiment, the processing circuit 1002 is configured to assessthe coverage of the target cell of the second frequency layer based onthe determined location and the coverage map by deriving from thecoverage map a signal strength or signal quality value for the secondfrequency layer corresponding to the determined location. The processingcircuit 1002 may be configured to derive the signal strength or signalquality value from the coverage map by receiving one of the followingfrom a network node comprising the coverage map:

the signal strength or signal quality value for the second frequencylayer, or

an offset which is a function of the signal strength or signal qualityvalue for the second frequency layer and the associated signal strengthor signal quality value for the first frequency layer.

The processing circuit 1002 is in one embodiment configured to determineto change to the target cell, when it is assessed that the target cellwill be received with a quality which is equal to or above a threshold.Furthermore, the processing circuit 1002 may be configured to perform anevaluation of mobility within the first frequency layer based on themeasurements on the cells of the first frequency layer, when it isassessed that the target cell will be received with a quality which isbelow the threshold. In another embodiment, the processing circuit 1002may be configured to issue an order to change to the target cell, whenit is determined to change to the target cell.

In an alternative embodiment, the measured cell of the first frequencylayer is a primary cell and the target cell is a secondary cell in amulti-carrier network. The processing circuit 1002 is in this embodimentadapted to determine whether to configure the secondary cell formulticarrier operation based on the assessment of the secondary cellcoverage.

An embodiment of a UE 1150 and a radio network node 1100 for a wirelesscommunication network deploying at least two frequency layers areschematically illustrated in the block diagram in FIG. 11. The UE 1150is configured to support cell change between frequency layers. The UE isfurther configured to be served in a cell of a first of the at least twofrequency layers by a radio network node and to perform measurements oncells of the first frequency layer and to exclude measurements on cellsof a second of the at least two frequency layers. The UE comprises aprocessing circuit 1151 configured to perform measurements on at leastone cell of the first frequency layer, and to determine a location ofthe UE based on results from the performed measurements. The processingcircuit is also configured to assess a coverage of a target cell of thesecond frequency layer based on the determined location and a coveragemap for the at least two frequency layers. The UE further comprises atransmitter 1152 configured to transmit information related to theassessed coverage of the target cell to the radio network node. Thetransmitter 1152 may be connected via an antenna port to a same or todifferent transmitting antennas 1158.

In one embodiment, the processing circuit 1151 is configured to assessthe coverage of the target cell of the second frequency layer byderiving from the coverage map a signal strength or signal quality valuefor the second frequency layer corresponding to the determined location.The transmitted information related to the assessed coverage of thetarget cell may comprise the derived signal strength or signal qualityvalue.

In one embodiment, the processing unit 1151 is configured to maintainthe coverage map in the UE. In an alternative embodiment, the UE furthercomprises a receiver 1153 configured to receive the coverage map fromthe radio network node. In this alternative embodiment, the UE need notmaintain the coverage map itself.

In another embodiment, the transmitter 1152 is further configured totransmit a capability to the radio network node, wherein the capabilityindicates that the UE supports assessment of coverage of cells of thesecond frequency layer without performing measurements on said cells.

The radio network node 1100 is configured to serve the UE 1152 in a cellof a first of the at least two frequency layers and to support cellchange between frequency layers. The cell change may comprise a cellreselection, a handover, or a connection release with redirection. TheUE is configured to perform measurements on cells of the first frequencylayer, and to exclude measurements on cells of a second of the at leasttwo frequency layers. The radio network node comprises a receiver 1101configured to receive information from the UE related to a coverage of atarget cell of the second frequency layer, and a processing circuit 1102configured to determining whether to change to the target cell based onthe received information. The receiver 1101 may be connected via anantenna port to a same or to different receiving antennas 1108.

The receiver 1101 is in one embodiment further configured to receive acapability from the UE, wherein the capability indicates that the UEsupports assessment of coverage of cells of the second frequency layerwithout performing measurements on said cells. The processing unit 1102may be configured to request information related to the coverage of thetarget cell to the UE, triggered by the received capability.

In another embodiment, the processing circuit 1102 is configured todetermine to change to the target cell when it is assessed that thetarget cell will be received with a quality which is equal to or above athreshold. The processing circuit 1102 may be further configured toperform an evaluation of mobility within the first frequency layer basedon the measurements on the cells of the first frequency layer, when itis assessed that the target cell will be received with a quality whichis below the threshold. In still another embodiment, the processingcircuit 1102 is further configured to issue an order to change cell whenit is determined to change to the target cell.

In an alternative embodiment, the measured cell of the first frequencylayer is a primary cell and the target cell is a secondary cell in amulti-carrier network. In this alternative embodiment, the processingcircuit 1102 is adapted to determine whether to configure the secondarycell for multicarrier operation based on the assessment of the secondarycell coverage.

An embodiment of a UE 1250 for a wireless communication networkdeploying at least two frequency layers is schematically illustrated inthe block diagram in FIG. 12. The UE is configured to support cellchange between frequency layers, to camp on a cell of a first of the atleast two frequency layers in idle mode, and to perform measurements oncells of the first frequency layer and exclude measurements on cells ofa second of the at least two frequency layers. The UE comprises a memory1251 and a processing circuit 1252 configured to perform measurements onat least one cell of the first frequency layer, and to determine alocation of the UE based on results from the performed measurements. Theprocessing circuit 1252 is also configured to assess a coverage of atarget cell of the second frequency layer based on the determinedlocation and a coverage map for the at least two frequency layers, andto determine whether to change to the target cell based on theassessment of the target cell coverage. In one embodiment, theprocessing circuit 1252 is configured to assess the coverage of thetarget cell of the second frequency layer by deriving from the coveragemap a signal strength or signal quality value for the second frequencylayer corresponding to the determined location.

In view of the above discussion, it will be appreciated that embodimentsof the above-described embodiments of the invention include methodsperformed at one or more nodes in a network, such as at an LTE eNodeB,for determining the coverage available to a UE from an unmeasured cellof one frequency layer, based on measurements of cells of otherfrequency layers. Various instances of these methods may also includesteps communicating measurement data or mapping data from one node toanother, again for the purpose of determining the coverage available toa UE from an unmeasured cell. As mentioned above, one or more of thesemethods may be based on measurement data received from the mobileterminals or UEs, including signal strength measurements, timingmeasurements, and the like, and may alternatively and/or also depend onidentification by the UEs of well-heard transmission points. It willalso be appreciated that the several techniques described above, as wellas their sub-processes, can be used in any combination unless it isobvious that that those techniques or sub-processes are inherentlyincompatible with one another. Other embodiments include similar methodsperformed at a UE. Still other embodiments include wireless nodeapparatus, such as a base station, and UE apparatus corresponding to themethods and techniques described above.

In some cases, the methods described above will be implemented in awireless transceiver apparatus such as the one pictured in FIG. 13,which illustrates a few of the components relevant to the presenttechniques, as realized in either a UE or a base station. Of course, itwill be appreciated that a network-based implementation need not belimited to a base station implementation, thus other radio network nodeapparatus configured to carry out the techniques described above arealso possible.

The apparatus illustrated in FIG. 13 includes radio circuitry 210 andbaseband & control processing circuit 220. Radio circuitry 210 includesreceiver circuits and transmitter circuits that use known radioprocessing and signal processing components and techniques, typicallyaccording to a particular telecommunications standard such as the 3GPPstandard for LTE-Advanced. Because the various details and engineeringtradeoffs associated with the design of such circuitry are well knownand are unnecessary to a full understanding of the invention, additionaldetails are not shown here.

Baseband & control processing circuit 220 includes one or moremicroprocessors or microcontrollers 230, as well as other digitalhardware 235, which may include Digital Signal Processors (DSPs),special-purpose digital logic, and the like. Either or both ofmicroprocessor(s) 230 and digital hardware may be configured to executeprogram code 242 stored in memory 240, along with radio parameters 244.Again, because the various details and engineering tradeoffs associatedwith the design of baseband processing circuitry for UEs and wirelessbase stations are well known and are unnecessary to a full understandingof the invention, additional details are not shown here

The program code 242 stored in memory circuit 240, which may compriseone or several types of memory such as read-only memory (ROM),random-access memory, cache memory, flash memory devices, opticalstorage devices, etc., includes program instructions for executing oneor more telecommunications and/or data communications protocols, as wellas instructions for carrying out one or more of the techniques describedherein, in several embodiments. Radio parameters 244 may include one ormore pre-determined tables or other data for supporting thesetechniques, in some embodiments.

Examples of several embodiments of the present invention have beendescribed in detail above, with reference to the attached illustrationsof specific embodiments. Because it is not possible, of course, todescribe every conceivable combination of components or techniques,those skilled in the art will appreciate that the present invention canbe implemented in other ways than those specifically set forth herein,without departing from essential characteristics of the invention.

What is claimed is:
 1. A method in a radio network node of a wirelesscommunication network deploying at least two frequency layers, whereinthe radio network node serves a user equipment in a cell of a first ofthe at least two frequency layers, the user equipment configured toperform measurements on cells of the first frequency layer, and toexclude measurements on cells of a second of the at least two frequencylayers, the method for supporting cell change between frequency layersand comprising: receiving information from the user equipment related toa coverage of a target cell of the second frequency layer, wherein theradio network node serves the user equipment in the cell of the firstfrequency layer, and the user equipment is configured to: performmeasurements on cells of the first frequency layer, exclude measurementson cells of a second frequency layer, and determine the informationrelated to the coverage of the target cell of the second frequency layerusing the measurements on the cells of the first frequency layer and acoverage map of the first frequency layer and the second frequencylayer, and determining whether to change to the target cell of thesecond frequency layer based on the received information.
 2. The methodof claim 1, further comprising: receiving a capability from the userequipment, wherein the capability indicates that the user equipmentsupports assessment of coverage of cells of the second frequency layerwithout performing measurements on those cells; and triggering a requestfor information related to the coverage of the target cell to the userequipment in response to receipt of the capability.
 3. The method ofclaim 1, wherein determining whether to change to the target cellcomprises determining to change to the target cell when it is assessedthat the target cell will be received with a quality which is equal toor above a threshold.
 4. The method of claim 3, further comprising, inresponse to it being assessed that the target cell will be received witha quality which is below the threshold, performing an evaluation ofmobility within the first frequency layer based on the measurements onthe cells of the first frequency layer.
 5. The method of claim 1,further comprising issuing an order to change to the target cell when itis determined to change to the target cell.
 6. The method of claim 1,wherein the cell change includes a cell reselection, a handover, or aconnection release with redirection.
 7. The method of claim 1: wherein acell of the first frequency layer on which measurements are taken is aprimary cell and the target cell is a secondary cell in a multi-carriernetwork; and wherein determining whether to change to the target cellincludes determining whether to configure the secondary cell formulticarrier operation based on the assessment of the secondary cellcoverage.
 8. The method of claim 1, wherein the information is a derivedvalue of the measurement of the second frequency layer.
 9. The method ofclaim 8, wherein the derived value of the measurement of the secondfrequency layer corresponds to a determined location of the userequipment on a coverage map of the second cell.
 10. The method of claim9, wherein the determined location of the user equipment is associatedwith the measurement of the first frequency layer.
 11. A radio networknode for a wireless communication network deploying at least twofrequency layers, wherein the radio network node is configured to servea user equipment in a cell of a first of the at least two frequencylayers and to support cell change between frequency layers, the userequipment being configured to perform measurements on cells of the firstfrequency layer, and to exclude measurements on cells of a second of theat least two frequency layers, the radio network node comprising: areceiver configured to receive information from the user equipmentrelated to a coverage of a target cell of the second frequency layer,wherein the radio network node serves the user equipment in the cell ofthe first frequency layer, and the user equipment is configured to:perform measurements on cells of the first frequency layer, excludemeasurements on cells of a second frequency layer, and determine theinformation related to the coverage of the target cell of the secondfrequency layer using the measurements on the cells of the firstfrequency layer and a coverage map of the first frequency layer and thesecond frequency layer; and a processing circuit configured to determinewhether to change to the target cell of the second frequency layer basedon the received information.
 12. The radio network node of claim 11:wherein the receiver is further configured to receive a capability fromthe user equipment, wherein the capability indicates that the userequipment supports assessment of coverage of cells of the secondfrequency layer without performing measurements on those cells; andwherein the processing unit is configured to, in response to receipt ofthe capability, request information related to the coverage of thetarget cell to the user equipment.
 13. The radio network node of claim11, wherein the processing circuit is configured to determine to changeto the target cell when it is assessed that the target cell will bereceived with a quality which is equal to or above a threshold.
 14. Theradio network node of claim 13, wherein the processing circuit isfurther configured to, in response to it being assessed that the targetcell will be received with the quality which is below the threshold,perform an evaluation of mobility within the first frequency layer basedon measurements on the cells of the first frequency layer.
 15. The radionetwork node of claim 11, wherein the processing circuit is furtherconfigured to issue an order to change cell when it is determined tochange to the target cell.
 16. The radio network node of claim 11,wherein the cell change includes a cell reselection, a handover, or aconnection release with redirection.
 17. The radio network node of claim11: wherein a cell of the first frequency layer is a primary cell andthe target cell is a secondary cell in a multi-carrier network; andwherein the processing circuit is adapted to determine whether toconfigure the secondary cell for multicarrier operation based on theassessment of the secondary cell coverage.
 18. The radio network node ofclaim 11, wherein the information is a derived value of the measurementof the second frequency layer.
 19. The radio network node of claim 18,wherein the derived value of the measurement of the second frequencylayer corresponds to a determined location of the user equipment on acoverage map of the second cell.
 20. The radio network node of claim 19,wherein the determined location of the user equipment is associated withthe measurement of the first frequency layer.